Sulfonimines

Triazole-fused pyridopyrimidines can be prepared by reaction of aldehydes with the substituted pyridopyrimidine 309 (Equation 106). The pyrazole-fused derivative 311 can be prepared by the reaction of the sulfonimine 310 with dimethyl acetylenedicarboxylate (DMAD) (Equation 107) <1998H(47)871>. 

Although of sufficient purity for the next step, the sulfonimine can be further purified by recrystallization. In a 2-L Erlenmeyer flask containing 150 mL of ethyl acetate is dissolved, with warming, 212 g of the crude sulfonimine. After the mixture is cooled to room temperature, about 400 nl. of pentane is added and the solution is allowed to stand at room temperature for 2-3 hr. The colorless crystalline product is collected by filtration, washed with 100 mL of pentane and air dried to give 191.5 g (78%), mp 78-80°C. The washings and filtrate are combined and the volume reduced by about one third using a rotary evaporator. A second crop of crystals, 20.2 g (8%), mp 75-79°C, was obtained on standing for several hours. 

This procedure is representative of a general procedure, for the synthesis of trans-2-sulfony1oxaziridines previously reported on a small scale (Table I). trans-2-(Phenylsulfonyl)-3-(p-nitrophenyl)oxaziridine was prepared on a 0.16-molar scale in greater than 85% yield. The Baeyer-Vill iger-type oxidation of the sulfonimine affords only the trans-oxaziridine. The synthesis of the sulfonimine (PhS02N=CHPh) directly from the sulfonamide and... 

Oxidation of chiral sulfonimines (R"S02N=CHAr)and chiral sulfamyl-imines (R RNS02N=CHAr)affords optically active 2-sulfonyloxaziridines and 2-sulfamyloxaziridines, respectively. These chiral, oxidizing reagents have been used in the asymmetric oxidation of sulfides to sulfoxides (15-68% ee), 11-13 selenides to selenoxides (8-9% ee] enolates to a-hydroxycarbonyl compounds (8-37% ee) and in the asymmetric epoxidation of alkenes (15-40% ee)... 

Reduction of A -sulfonimine 102 with LAH affords a 60 40 mixture of transxis reduced bicyclic perhydro-l,2-thiazines 103 and 104 in 85% combined yield (Equation 10) <1998CJC164>. In contrast, the NaBH4 reduction of bridged bicycle 105 affords compound 106 as a single diastereomer (Equation 11) <2002HCA1973>. 

Both isomeric forms of (+)- and (—)-(camphorylsulfonyl)oxaziridines are available by oxidation of the corresponding sulfonimines with buffered potassium peroxymonosulfate (oxone). Since oxidation can only take place from the endo-fa.ce of the C=N double bond due to steric blocking of the exo-face, a single oxaziridine isomer is obtained. The enantiomerically pure sulfonimines can be prepared in three steps in better than 80% yield from inexpensive (+)- and (—)-camphor-10-sulfonic acids. Alternatively they are commercially available200. 

Note, however (see Appendix), that the HO(A)-LU(acraldehyde) energy gap is slightly smaller than the HO(propene)-LU(sulfonimine) energy gap. Hence rule 2 should always be applied with caution. 

Examples of imine allylation in aqueous media are rather limited compared with the carbonyl version. This is ascribed to the lower electrophilicity of the C=N function of imines and its ease of hydrolysis to carbonyl compounds. In order to overcome the undesired side-reactions, sulfonimines in place of simple imines are success-fully used for the allylation under aqueous conditions (Equation (61)). Grotylation of cr-sulfonimino esters gives... 

Allylation of aldimines and sulfonimines with indium powder in poly(propylene) glycol (MW 1000), a benign and recyclable reaction medium, results in the formation of the corresponding homoallylic amines and sulfonamides in high yields (Equation (62)).265... 

Table 10 Indium-mediated crotylation of sulfonimines. Reproduced with permission from ACS Publications...

When bis[2,2,3,3-tetrafluoropropoxy] tellurium difluoride was heated with two molar equivalents of JV,(V-bis[trimethylsilyl]benzenesulfonamide at 115°, tellurium bis[benzene-sulfonimine] was formed1 (see p. 77). 

Although no report has appeared on the direct oxidation of sulfinimines, studies have indicated that sulfonimines 106 were probably obtained on oxidation of sulfenimines 104 with excess m-CPBA via the intermediate sulfinimines 105.70,71... 

Further oxidation of sulfonimines 106 gave AAsulfonyloxaziridines 107, a versatile class of neutral, aprotic, chiral oxidizing reagents.72,73... 

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